Fermi surface and extended van hove singularity in the noncuprate superconductor Sr₂RuO₄

We mapped the Fermi surface of the first copper-free layered perovskite superconductor, Sr2RuO4, by high-resolution (∼22 meV) angle-resolved photoemission. Three bands cross the Fermi energy, consistent with band structure calculations; one around γ− and two around X−. The highlight is the observation of an extended van Hove singularity located 17 meV below the Fermi level. It extends around M− for ∼0.2 Å−1 along γ−-M−-γ− and X−-M−-X− in the projected Brillouin zone. This raises important questions related to the possible role of a van Hove singularity for oxide superconductivity. © 1996 The American Physical Society.